Two ecological systems, evolved for thousands of years in near total isolation from each other, suddenly thrust together, flooding each side with the organisms of the other over the course of nearly five centuries—this is the concept of the Columbian exchange, a term coined by historian Alfred W. Crosby in 1972 to describe the biological intermingling of the Old World and New World in the centuries following the first contacts of Europeans, Africans, and indigenous Americans.
Encompassing all classes of animals, plants, and microbes, and the attendant cultural and social transformations they engendered, the Columbian exchange forever transformed the face of the planet and represents one of the most important consequences of the European encounter with the Americas.
Plants comprised one broad category of this centuries-long biotic exchange. In 1951, Russian botanist Nikolai Ivanovich Vavilov listed 640 of humanity’s most important cultigens. Of these, more than 500 originated in the Americas.
Among the most important staple crops of the Western Hemisphere to make their way to Europe, Africa, and beyond were maize, beans (of many varieties), potatoes and sweet potatoes, squashes and pumpkins, peanuts, and manioc (cassava).
Also important were the papaya, guava, avocado, pineapple, tomato, chili peppers of many varieties, and cacao. Maize cultivation originated in Mesoamerica around 5000 b.c.e. before spreading to both South and North America at least 1,000 years before the European arrival.
The most important staple crop of the Americas, maize soon became one of the most important cultigens in both Europe and Africa. Beans, of which there are more than a thousand species, formed one pillar of the maize-beans-squash triad of staple crops common among many pre-Columbian American cultivators.
Not all beans are American in origin—soybeans, for instance, originated in the Eastern Hemisphere—but many of the most popular varieties are American, including the lima, Rangoon, kidney, navy, snap, and frijole beans (pinto, red, black, and others).
Potatoes, indigenous to the Andes, were developed into hundreds of varieties in the centuries before 1500. After the conquest of Peru, Spaniards selected several varieties to transport back home, particularly the white potato, which soon spread across much of Europe.
Wealthier classes tended to look upon the potato as a quasi-food, while for many of the poor it became an important staple crop, most infamously in Ireland, where overreliance on a few varieties led to the Irish famine of the 1840s. Another tuberous American starch was manioc.
Known in its form as tapioca pudding among many Europeans, and as cassava across much of Africa and Asia, where it became an important staple crop and famine food, manioc has very little nutritional value but grows where many other cultigens will not, thriving in a broad belt extending 30 degrees north and south of the equator.
Far and away the most important nonfood cultigens transferred from the Americas to the Old World were tobacco and coffee, both of which rapidly became extremely popular in Europe before their subsequent spread across the globe. Also important were some varieties of cotton, and, from the 19th century, rubber.
The most important plant crops making their way from the Old World to the Americas included wheat, rice, bananas, sugar, grapes, olives, mangos, breadfruit, and African yams. Also important were chickpeas, melons, onions, cauliflower, cabbage, lettuce, and radishes. European fruits transplanted to the New World included oranges, lemons, pomegranates, citrons, and figs. Wheat was taken to New Spain soon after the conquest of Mexico.
By 1535, New Spain was exporting wheat to the Caribbean and beyond, while wheat cultivation soon spread to wherever conditions permitted. Bananas were taken to the Antilles from the Canary Islands in 1516, after which banana cultivation spread rapidly throughout the Caribbean Basin and beyond.
Sugar, originating in the Mediterranean and cultivated in the Canary Islands and Azores in the 1400s, was taken to Hispaniola in 1493 by Columbus. Its subsequent spread in the Spanish Antilles was slow until the Spanish Crown intervened actively to promote its cultivation, while its spread in Brazil was due mainly to the actions of planters.
Grape cultivation, overwhelmingly for wine production, met many obstacles in the Caribbean and New Spain but proved successful in Peru and Chile; by the 1650s, they were producing wine for export. Olives followed a similar path, with initial failures in the Antilles and New Spain followed by success in Andean highland valleys.
Another category of plants consisted of weeds, plants for which people had not devised a use, and whose exchange across the Atlantic was unintended; examples include the dandelion, daisy, and Kentucky bluegrass. Though no definitive study has determined the precise number of such species exchanged, there is little doubt that it runs into the thousands.
The introduction of cattle, pigs, sheep, and goats also profoundly affected peoples and cultures across the Americas, with important regional variations. Pigs proliferated across the Caribbean from early on, and there were few places thereafter where abundant pigs did not accompany both Spanish and Portuguese or were not adopted by indigenous Americans.
Cattle ranching emerged as an important economic pillar across much of the hemisphere, with beef, hides, and tallow becoming major commodities across most of the Americas save the Amazon Basin and the Andes. Sheep thrived especially on the high plateau of Central Mexico and Rio Grande Basin, the Andes, and across southern South America.
Native peoples were quick to adopt whatever of these animals the environment permitted, generating widespread variations across the hemisphere. The unintended consequences of sheep and cattle proliferation in some regions included widespread overgrazing and soil erosion.
During the colonial period, the environmental effects of unrestrained sheep herding in central and northern Mexico were especially deleterious. Animals unintentionally taken to the Americas by Europeans included thousands of species of insects, rats, and a variety of other vermin.
Animals comprised another broad category of organisms exchanged between Old World and New. The pre-Columbian Americas had no beasts of burden save the camelids of the Andes, the llama and alpaca. Other domesticated New World animals included the guinea pig, dog, turkey, and duck.
European introductions included horses, donkeys, mules, cattle, oxen, pigs, sheep, goats, chickens, and many varieties of larger dogs. While many indigenous peoples rejected wheat and other European crops, many also readily adopted these four-legged European domesticates.
The horse, several varieties of which had evolved in the Americas and become extinct at the beginning of the Holocene, exercised a profound influence across the hemisphere. From the Argentine pampas to the Great Plains of North America, horses and their kin transformed fundamental aspects of society and culture, beginning with their introduction into the Antilles by Christopher Columbus in 1493.
Herds of wild horses spread quickly north after the conquest of Mexico, reaching the Great Plains by the mid-1700s and perhaps before. The introduction of horses to South America is generally attributed to Pedro de Mendoza’s few animals taken to Buenos Aires in 1535. Fifty years later, vast herds populated the vast open prairies of the pampas.
A final and monumentally important category of organisms exchanged between Old World and New consisted of microbes. While the vast majority were harmless, a handful were deadly pathogens responsible for one of the most precipitous and widespread demographic declines in world history.
The overwhelming direction of the flow of disease was from Europe to the Americas. By the 16th century, after centuries of plagues and epidemics, European peoples inhabited a highly evolved disease pool in which immunities to the most virulent pathogens were widely shared.
Such immunities did not exist in the Americas, although a wide variety of diseases were endemic in the Western Hemisphere, including tuberculosis, histoplasmosis, leishmaniasis, Chagas’ disease, amebic dysentery, various rickettsial fevers, syphilis, and many types of intestinal parasites. Of the diseases transplanted from Europe to the Americas, smallpox was the deadliest killer, along with typhus, measles, bubonic plague, and malaria.
The one pathogen that migrated the other way was syphilis, a disease and a process of transmission that spawned a huge body of literature and debate. A broad scholarly consensus emerging from this debate holds that both venereal syphilis and an endemic nonvenereal strain (caused by various strains of the bacterium Treponema pallidum) were most likely first contracted by European men through sexual relations with indigenous women and spread by the captured Indians taken to the Spanish court by Columbus in 1493.
It is believed that the epidemic that spread among the men of Christopher Columbus at the garrison of Isabela on Hispaniola in 1493 during the conquest of the Caribbean was a form of syphilis, probably contracted through the rape of Indian women.
The disease was unknown in Europe before 1493. By 1496, it had spread to France, Germany, Holland, Switzerland, and Greece, and by 1503, to China, spreading farther and becoming endemic thereafter.
In sum, scholarly debates and investigations continue on these and many other environmental and biological consequences engendered by the coming together of Europe, Asia, Africa, and the Americas after 1492.